What are the differences between colds, flu and COVID-19?

It's a common pattern - after barely suffering a sniffle all summer, you find yourself coughing and sneezing your way into autumn. Whether it's just a cold or (in more serious cases) flu, there's always an uptick in cases as it gets colder.

It isn't entirely clear why colds and flu are more common in the autumn and winter, but scientists do have a few ideas. Cold weather may influence the way our immune systems deal with viruses. A lack of humidity in the air may help these viruses thrive. And since we spend more time indoors, we may come into contact with more people who are harbouring infections.

Unfortunately, this winter we'll be dealing with another nasty on top of the usual suspects. At this stage, it's hard to say how colder temperatures will affect transmission of COVID-19, but we do know there's everything to play for in terms of avoiding a second wave.

We might also expect things to get confusing. With so many different bugs doing the rounds - each with fairly similar symptoms - it may be hard to know whether you're dealing with a cold, the flu, or COVID-19.

"All of these infections involve a cough, sore throat, fatigue, aches and pains," says Dr Stephanie Colbourn, a GP at the Portland Medical Centre in South Norwood. "The key to telling the difference between them is by which symptoms are predominating."

It's crucial to remember, though, that no diagnosis based on symptoms alone is 100% accurate, and if you have any symptoms that might be due to COVID-19, it's essential to self-isolate, arrange a test as soon as possible, stay in isolation until you have the results and follow the instructions you're given if your test is positive. If your test is negative, you can leave self-isolation as soon as you feel better.

If it's just a cold ...

If it's just a cold, the symptoms tend to stay in the upper airways, meaning you're most likely to experience a blocked nose, sneezing and a sore throat. You will probably feel OK in yourself otherwise, though there may be a sense of malaise or being run down.

"The mucus production can lead to a cough that feels 'wet' but that does not mean that it is necessarily a chest infection. Other symptoms can include aches, pains and fatigue," says Dr Colbourn.

There are 200 different viruses known to cause colds, many of which belong to the rhinovirus family. In some cases, the culprit is a type of coronavirus, though thankfully not the same type that causes COVID-19. Most colds will go away by themselves in a week or so without treatment, but in the meantime you can take over-the-counter remedies to relieve the symptoms.

If it's the flu ...

Flu (also known as influenza) is typically more serious than a cold, and can lead to complications such as pneumonia in vulnerable people. Caused by a number of different influenza viruses, it can affect both the upper and lower respiratory system, and tends to last a week or two - though the fatigue may persist a bit longer.

"The flu tends to cause more whole-body symptoms rather than upper airway symptoms, like fever, fatigue, aches and pains, and headaches. However, you can experience some dry cough and a sore throat," says Dr Colbourn.

Each year, people at risk of complications are offered a flu vaccine on the NHS. This year even more people will be eligible for a free flu vaccination. If you fall into this category, it's a good idea to get vaccinated in the autumn before flu season starts. You may also be able to get vaccinated privately - for example through your pharmacist.

If it's COVID-19 ...

COVID-19, which is caused by a new type of coronavirus, can be extremely serious in some people, while only causing mild (or no) symptoms in others. Because of the risk of passing it on to vulnerable people, it's vital to contain its spread, even if you’re at low risk of serious illness yourself.

"A key difference with COVID-19 is that a fever and dry cough are the main symptoms," says Dr Colbourn. "Another difference is that COVID-19 can cause shortness of breath and the loss of the sense of taste and smell (anosmia). These can be accompanied by fatigue, aches and pains."

While the list of possible symptoms is long, the main three are fever, dry cough and anosmia.

"If you develop any of these symptoms, please self-isolate immediately," says Dr Colbourn. "This helps prevent the spread of the virus that could cause a severe form of the illness in people with weaker immune systems." You can use our coronavirus checker to find out what to do next.

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If you're worried ...

Unfortunately, if your symptoms are vague, there's really only one way to put your mind at rest, and that's to get tested.

The NHS provides COVID-19 tests free of charge, and advises that you need to get the test done in the first five days of having symptoms. You can either book a visit to a test site, or order a home test.

"If you need results quicker or have special requirements then a private test can return results within 24 hours and costs under £250," says Dr Mark Ali, medical director of the Private Harley Street Clinic.

While the UK's testing capacity has been under scrutiny since the outset, the aim is to get to 500,000 tests a day by the end of October. The government also plans to roll out rapid swab tests across hospitals and care homes. These new swab tests - which only take 90 minutes to process - have the ability to check for flu and other viruses as well as COVID-19. This should be extremely helpful as we head into flu season.

"We recognise that there will be a substantial increase in demand for testing as we approach the traditional cold and flu season," says Dr Ali. "However, there is no workaround for this - only testing can provide clarity and protect not only you, but also the broader society around you."

Dr Colbourn adds that, if your GP practice provides access to a digital triage platform, it's a good idea to make use of this resource. Otherwise, you can seek help via 111, which will direct you towards the appropriate healthcare resource.

In the meantime, it's important to reduce your risk of catching COVID-19 (and maybe colds and flu too) by following the existing guidelines.

"Please continue to wear a mask, wash your hands frequently and adhere to social distancing guidelines when in public to help mediate the potential impact of a second peak of COVID-19 cases," she says. "Also, when in doubt, speak to your local pharmacist. They are amazing sources of information!"